of Human Monstrosity . 245 



a loop, which ramifies with the subdivisions of the tube, and thus 

 the groundwork of the liver is formed, to which the parenchyme 

 is gradually super-added. The ramifying vein is the Vena Portae : 

 the original venous stem, as it advances to the heart, receives the 

 collection of returning veins from the liver, and is the center to 

 which the ascending cava is afterwards directed. 



Before the first, circulation through the vascular area is fully 

 established, the heart does not pulsate, but has only a vermicular 

 motion from one end to the other. The blood in the aorta un- 

 dulates, as in the dorsal vessel of insects, and has a different 

 direction in different parts of the tube. In this way it seems 

 gradually to overcome the obstructions to its direct course, and 

 the first circulation is established. Numerous veins of the vascular 

 area soon collect around the subdivisions of the omphalo-mesen- 

 teric artery : they form a trunk which returns to the body, in 

 company with that artery. They separate on reaching the intes- 

 tine, and the vein turns upwards, to become a principal root of 

 the Vena Porta?. This omphalo-mesenteric vein is considered by 

 many as the first vessel which ramifies within the body of the 

 embryo. 



The first circulation having been established, the arteries sub- 

 divide in the soft substance of the body. For instance — the 

 contents of the posterior extremity of the aorta have an undu- 

 lating motion until the artery returns upon itself and forms a 

 loop : the advancing part of the loop is an artery, the returning 

 part a vein. From the convexity of the loop another loop is 

 gradually formed, and then another. So that one side of the chain 

 of loops at length forms a continuous arterial, and the other a 

 continuous venal stem; and the transverse portions of the loops 

 are anastomosing branches. It seems that the smaller veins are 



